Current wireless communication systems provide the ability for users to communicate to and from wireless or mobile users. There are generally two types of wireless communication systems, circuit-switched (CS) and packet-switched (PS).
In typical circuit-switched wireless communication systems, the Mobile Switching Center (MSC) connects the landline Public Switched Telephone Network (PSTN) system to the wireless communication system. The MSC is typically split into an MSC server and a Media Gateway (MGW), and incorporates the BICC (Bearer Independent Call Control) or ISUP (ISDN User Part) call control protocol for call delivery between MSCs.
The current approach to introducing Internet Protocol (IP) Multimedia services for Universal Mobile Telecommunications Service (UMTS) and Code Division Multiple Access (CDMA) Third generation (3G) systems is to define a brand new IP Multimedia Subsystem (IMS), comprised of a set of IP-connected network entities within the IMS using packet-switched services. These network entities provide IP Multimedia features and services using the Session Initiation Protocol (SIP) as the primary vehicle for call control.
The IMS shares little in common with the traditional MSC supporting circuit-switched services. Thus new capabilities and services must be defined, developed and deployed twice for systems supporting both circuit-switched and IP Multimedia services.
Therefore, a need exists for a communication system that supports features and services for mobile units using either circuit-switched or packet-switched communication systems.